VOL. 5, No. 4 MERCURY AND ITS COMPOUNDS IN ANCIENT TIM- 419

MERCURY AND ITS COMPOUNDS IN ANCIENT TIMES*

EARLS R. CALEY, COLUMBUS, OHIO

The peculiar and striking properties possessed by metallic mercury exercised a special influence on the beginnings of chemical thought. This element captivated the imaginations of the ancients and played a major rble in the fantastic doctrines of the alchemical art. The date of the first knowledge of mercury can be set back considerably farther than most historians of chemistry have generally believed. The earliest find of the metal itself was made by Schliemann during his Egyptian travels to Kurna.' This archaeologist unearthed a small flask of the metal, along with other objects of technical interest, in a tomb dating back to 1500-1600 B.C. This is the sole evidence of the knowledge of the metal among the ancients until we come to the Greeks. Other facts, such as the probable antiquity of some of the recipes of the Leyden Papyrus employing mercury, tend to show that the metal was known in Egypt a t this early date.

The earliest written evidence of a definite date concerning mercury is given by Aristotle who refers to it as a "fluid s i l~e r . "~ A method of obtaining mercury from the native sulfide is given by Theophrastus, who state^,^

Such is the production of quicksilver, which has its uses This is obtained from cinnabar rubbed with vinegar in a brass mortar with a brass pestle.

This passage is also the first evidence of the process of amalgamation. Dioscorides, writing a t about the beginning of our era, describes the

recovery of mercury by distillation. This primitive method and rudi- mentary distilling arrangement is about the earliest reference to this im- portant chemical operation. The account reads thus:4

Quicksilver is made from "ammion," which is called cinnabar. An iron bowl con- taining cinnabar is put in an earthen vessel and covered with a cup-shaped lid smeared with clay. Then it is set on a fire of coals and the soot which sticks to the cover, when wiped off and cooled, is mercury.

The same author also refers to native mercury in the same passage: Quicksilver is also found in drops falling from walls of silver mines. Some say

there are quicksilver mines.

Among the Latin writers, Vitruvius and Pliny both give interesting refer- ences to this metal. Evidently the Romans made a distinction between native mercury and that prepared artificially from cinnabar, for the for-

* Paper read before the Division of History of Chemistry a t the 74th Meeting of the American Chemical Society a t Detroit, Mich., September 8, 1927.

' von Lippmann, "Entstehung und Ausbreitung der Alchemie." p. 001. Meteorlogica IV, 8, 11.

"'On Stones" (from p. 139 01 Hill's translation). ' Materia Medica V, 70.

mer was termed "argentum vivum" or quicksilver, while the latter was called "hydrargyrum" meaning, literally, silver water. Thus in this case they made a distinction between substances chemically identical, whereas in so many other cases they classed chemically different substances under the same name, all as a result of their unscientific classification of the various forms of matter.

Vitmvius gives us some valuable information as regards the early knowl- edge of mercury. This author describes the recovery of mercury from the ore, both in the native state and by a aude method of smelting, in the following passage?

Minium is an ore. During the digging it sheds tears of quicksilver which the miners collect and save. The masses of ore as they are taken from the mines are so full of moisture that they are thrown into a furnace or oven in the workshop to dry, and the fumes that are driven off from them by the heat of the fire, settle down an the floor of the oven and are found to he quicksilver. When the lumps of ore are taken out. the drops which remain are so small that they cannot be gathered up, hut they are swept into a vessel of water, and there they run together and combine into one.

Vitmvius also records some interesting observations on the density of mercury, stating:=

If quicksilver be placed in a vessel and a stone of a hundred pounds weight be plsced on it, i t will swim at the top, and notwithstanding its weight, be incapable of pressing the liquid so as to break or separate it. If this be taken out, and only a scnrple of gold be put in, that will not swim, but will immediately descend to the bottom. This is a proof that the quantity of body does not depend upon its weight but upon its nature.

Certainly this is an experiment in physics undertaken with the true scien- tific attitude. The distinction between mass and weight is clearly stated here for the first time as far as our existing records show. Vitmvius is also the first one to mention the fact that mercury unites with gold, and the first author to mention the employment of mercury for recovering gold. His statement on amalgamation is this:'

Onicksilver is used for many ourrroses: without i t neither silver nor brass can be - ~. . properly gilt. When gold is embroidered on a garment which is worn out and no longer fit for use, the cloth is burnt over a fire in earthen pots; the ashes are thrown into water and quicksilver added to them; this collects all the particles of gold and unites with them. The water is then poured off and the residuum placed in a cloth, which when squeezed with the hand, suffers the liquid quicksilver to pass through the pores of the cloth, but retains the gold in a mass within it.

It is rather probable that amalgamation with gold was discovered earlier than this date (1st century B.C.) but this account of Vitruvius, just quoted, is the earliest known reference to the process.

De Architectura, VII, 8. "bid., VII, 8. 7 Ibid., VII, 8.

VOL. 5. No. 4 MERCURY AND ITS COMPOUNDS IN ANCIENT TIMES 421

Pliny's statements on mercury and cinnabar are clear and free from ambiguity. Concerning native quicksilver and its properties, he writes?

There is a mineral found in these veins of silver, which yields a humor that is always liquid, and is known as quicksilver. I t acts as a poison upon everything, and pierces vessels even, making its way through them by the agency of its malignant properties. All substances float upon the surface of quicksilver, with the exception of gold, this heing the only substance it attracts to itself. Hence i t is, that it is such an excellent refiner of gold; for on being briskly shaken in an earthen vessel with gold, i t rejects all the impurities that are mixed with it. When once i t has expelled these superfluities, there is nothing to do but to separate i t from the gold; to effect which i t is poured upon skins which have been well tawed, and so exuding through them like a sort of perspiration, it leaves the gold in a state of purity behind.

It is evident that amalgamation was a well-recognized phenomenon in Pliny's time. The last passage is one of our earliest references to filtra- tion as a means of separating substances. In another passage Pliny gives the method of preparing mercury from the ore. It will be remembered that the Romans considered the metal obtained in this way as being dif- ferent from native mercury or even inferior to it, andgaveit another name. The methods of obtaining mercury from cinnabar in ancient times were, according to Pliny, these:*

Human industry has also discovered a method of extracting hydrargyros from the inferior minium, a substitute for quicksilver, the further mention of which was deferred, a few pages before, to the present occasion. There are two methods of preparing this substance: either by pounding minium and vinegar with a brazen pestle and mortar, or else by putting minium into flat earthen pans, covered with a lid, and then enclosing it in an iron seething pat well luted with potter's clay. A fire is then lighted under the pans, and the flame kept continuously burning by the aid of the bellows; which done, the steam is carefully removed, that is found adhering to the lid, heing like silver in color, and similar in its fluidity. The liquid, too, is easily made to separate in globules, which, from their fluid nature, readily unite.

Apparently the chief use of mercury in Grecian and Roman times was in gilding. There is no evidence showing that amalgamation was applied to obtain gold from its ores as early as this period, although this may have been done on a small scale, since gold was so recovered from garments embroidered with the metal.

Among the recipes of the Leyden Papyrus X are a number that em- ploy mercury as an ingredient. There can be no doubt, from the evidence in this document, that the Ancients were acquainted with a considerable number and variety of mercury amalgams, both simple and complex. It has been seen that the fact that gold would unite with mercury was

Natural History, Bk. XXXIII, chap. 32 "bid., Bk. XXXIII, chap. 41.

known in the time of Vitruvius. Several of the recipes in this manuscript give preparations of gold amalgam. This is typical:'"

No. 54-Preparation of Gold Liquid-Place the leaves of gold in a mortar, pulwr- ize them with mercury and it is done.

There are no recipes in this document that give the preparation of silver amalgam, and as far as the evidence shows, this amalgam does not seem to have been prepared in ancient times. The fact that copper would unite with mercury was well known. A process in which this knowledge was applied to use is the following:

No. 54-Coating of Copper-If you desire that copper shall have the color of silver; after having purified the copper with care, place it in mercury and white lead; mercury alone suffices for coating it.

Tin amalgam was also a well-known product. The recipe quoted here was a preparation intended to give copper objects a silvery appearance and is clearly a simple tin amalgam. The text reads:

No. 27-Coloring in Silver-For silvering objects of copper; tin in sticks, 2 drachmas; mercury, 2 drachmas; earth of Chios, 2 drachmas. Melt the tin, throw on the crushed earth, then the mercury, and stir with an iron and fashion into globules.

There are also several recipes in this papyrus in which mercury was com- bined with two or more metals to form complex amalgams, the object being, of course, to form imitations of silver or electrum. It is certain from these various processes that the preparation of amalgams was well understood as an art in ancient times.

Apparently the only compound of mercury known to the Ancients was the native sulfide, cinnabar. The records show that this was widely em- ployed as a pigment and as a source of metallic mercury. The striking color of this substance must have attracted the attention of primitive men had they seen any of this rather rarely occurring mineral, but our earliest definite record is given by Theophrastus, when he describes the preparation of mercury from it. The next record in point is left by Vitru- vius. This author devotes considerable space to the means of employing the compound for purposes of decoration. Apparently, the pigment was very often applied to interior walls by incorporating i t with wax. Of special interest from the chemical point of view is the method used to de- tect admixtures of chalk with the pigment, minium. Although there is some doubt as to whether this test was applied to red lead or to the native mercuric sulfide, since the Ancients frequently confused the two, i t is more probable that it was the true minium that was adulterated with chalk. The method of detecting the presence or lack of this adulterant is given in these words by Vitruvius,"

10 This recipe and those following are from the writer's "The Leyden Papyrus X; an English Translation with Brief Notes," THIS JOURNAL, 3, 1149-GG (Oct., 1926).

De Architectma, VII, 12.

For recognizing this fraud, i t is necessary to place the minium on a sheet of iron which is heated to incandescence. If then, the minium, which was red, becomes black and on cooling regains its former color, one can be assured that i t was not adulter- ated.

The mercuric sulfide, if pure andnot heated too strongly, would act in this way, partly subliming in the black form, and on cooling be changed back to vermilion, especially if ground up again. If, however, some chalk was mixed with the pigment, this adulterant would be decomposed, partly a t least, into carbon dioxide and lime in the heating with the result that the latter compound would act upon the mercuric sulfide, decomposing i t and leaving a permanent black color due to the liberated mercury. Naturally the ancients did not connect any such explanation with their empirical test, but nevertheless, i t is evident that the test that they did apply to detecting the adulteration was a rational and effective one from the chemical point of view.

The Greek writer, Dioscorides, also gives some information on native mercuric sulfide, but this author confuses the mineral with red lead and with the resin, dragon's blood, so that his accounts are somewhat lacking in definiteness and clarity.

Pliny makes some interesting statements on minium. Concerning its sources and occurrence, he says:'%

It is also in silver mines that minium is found, a pigment held at the present day in very high estimation; and by the Romans in former times-used for sacred purposes as well. . . . . . ior my own part I am quite a t a loss to account for the origin of this usage; but i t is a well-known fact, that at the present day even, minium is held in great esteem with the nations of Ethiopia, their nobles being in the habit of staining their bodies all over with it.

And again,13

According to Juba, minium is also a production of Carmania, and Timagenes says it is found in Ethiopia. But from neither 'of these regions is i t imported to Rome, nor, indeed, from hardly any other quarter hut Spain; that of most note coming from Sisapo.

It is interesting to note that this latter locality is identical with the present district of Almaden, still famous as a chief source of the mineral cinnabar.

The fact that this mercury compound is poisonous was well recognized in ancient times in spite of the fact that it was sometimes used in medicinal preparations. On this subject Pliny says:I4

As it is a fact generally admitted, that minium is a poison, I look upon all the re- cipes given as highly dangerous which recommend its employment for medicinal pur- poses.

Natural History, Bk. XXXIII, chap. 36. 13 Ibid., Bk. XXXIII, chap. 40. " Ibid., Bk. XXXIII, chap. 41.

Pliny also makes another statement of interest on the poisonous properties of the dust from this pigment:ls

Persons em~loved in the manufactories in reo oar in^ minim Dmtect the face with . . . masks of loose bladder skin in order to avoid inhaling the dust which is highly pernicious; the covering being at the same time transparent enough to admit of being seen through.

This was assuredly the forerunner of our modern dust and gas masks. The synthetic preparation of mercuric sulfide for pigment or other uses

was probably unknown to the ancients. The preparation of this and other mercury compounds was added to the list of known substances during the Middle Ages but i t seems certain that the native sulfide was the only compound of mercury known at this early date.

lS Natural History, Bk. XXXIII, chap. 40.